Convex lens of 10 cm focal length is combined with a concave lens of 6 cm focal length. Find the focal length of the combination.
Correct answer: B. - 15 cm
- A. 15 cm
- B. - 15 cm
- C. 30 cm
- D. - 30 cm
Explanation
When combining lenses, the focal length of the combination is calculated using the formula 1/f = 1/f1 + 1/f2. In this case, the focal lengths of the convex and concave lenses are +10 cm and -6 cm respectively. Plugging these values into the formula, we get 1/f = 1/10 + 1/-6, which results in f = -15 cm. This negative sign indicates that the combination acts as a diverging lens.The other options are incorrect because they do not consider the signs of the focal lengths when combining lenses, leading to miscalculations.
Report an error
The more specific you are, the faster it gets fixed. A source beats an opinion.
Prefer email? [email protected]
About Optics
Light is studied through reflection, refraction, dispersion, interference, diffraction and polarization, linking ray behavior with its wave nature. Questions may involve mirrors, lenses, optical instruments, refractive index and image formation, while geometrical optics deals with rays and wave optics explains effects such as interference and diffraction.
Practise Optics
665 free Optics MCQs from Physics, each with the correct answer and an explanation. Unlimited attempts, no account needed.
Discussion
Stuck on an option, or know a faster way to get there? Ask or explain it here.
No comments yet. Be the first to explain this one.
Exams that ask Physics questions like this
Physics is on 11 papers prepared for on TestUstad, and all of them draw the same bank, so this question is worth knowing for every one of them.
More Optics questions
If f1 = 12 cm, f2 = -18 cm, find the maximum focal length of the combination.
What is the number of images of an object formed by two mirrors if the angle between the mirrors is between 2π/4 and 2π/5?
Let x and y be the distances of the object and image formed by a concave mirror from its focus and f be the focal length, then:
The focal length of a convex lens with a refractive index of 1.5 is 2 cm. The focal length of the lens, when immersed in a liquid of refractive index 1.25, will be:
The time required for light to pass through a glass slab of 2 mm thickness is (µglass=1.5)
If the tube length of an astronomical telescope is 105 cm and magnifying power is 20 for the normal setting, calculate the focal length of the objective.